Protected Carbon Steel Pipe for Fire Tube Heat Exchange Devices, Particularly Boilers

ABSTRACT

A protected carbon steel pipe for fire tube heat exchange devices, particularly boilers, comprising internally, at least along a portion of its length, at least one bonded layer of corrosion-resistant material.

The present invention relates to a protected carbon steel pipe for fire tube heat exchange devices, particularly boilers.

BACKGROUND OF THE INVENTION

It is known that fire tube heat exchange devices exist which provide pipes designed to convey flue gases generated by combustion in appropriate furnaces, such pipes being provided within a vessel which contains the fluid to be heated; among such devices, boilers for generating hot water or another heat transfer fluid are particularly important.

The pipes comprised within said devices are made of carbon steel in order to ensure optimum quality of the welded joints between the pipes and the structures of the devices, which are also made of carbon steel; however, in the case of devices, such as for example condensing boilers, in which the water vapor contained in the flue gases condenses inside the flue gas conveyance pipes, condensation forms which attacks strongly by corrosion the wall of the pipes.

Pipes of the described type are not typical only of boilers, but can be present also in other devices of industrial thermal cycles, such as for example condensers, economizers and heat exchangers.

SUMMARY OF THE INVENTION

The aim of the present invention is to provide a carbon steel pipe adapted to convey flue gases which is entirely protected against the danger of corrosion caused by condensation and further ensures high efficiency in the transmission of heat from the flue gases to the fluid, and in particular to the water, to be heated.

The proposed aim is achieved by a protected carbon steel pipe for fire tube heat exchange devices, particularly boilers, according to the invention, characterized in that it comprises the features disclosed in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages will become better apparent from the description of some preferred but not exclusive embodiments of the protected carbon steel pipe for fire tube heat exchange devices, particularly boilers according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view of a fire tube boiler with a pipe according to the present invention;

FIG. 2 is a partial sectional view, taken along the line II-II of FIG. 1;

FIGS. 3 to 25 show the same sectional view according to variations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the FIGS. 1 and 2, the reference numeral 1 generally designates a fire tube boiler with a burner 2, a furnace 3, a flue gas reversal chamber 4 a, a vessel 5 which contains the water to be heated with couplings 5 a, 5 b respectively for inflow and outflow, pipes 6 designed to convey the gases generated by combustion in the furnace which arrive from the reversal chamber 4 a and are sent to the output chamber 4 b according to the arrows shown in FIG. 1.

The boiler 1 is of the type known as condensing boiler, and therefore the water vapor contained in the flue gases condenses therein as they flow within the pipes such as 6; the structure of said boiler is made of carbon steel.

An important characteristic of the invention consists in that the pipe 6 is made of carbon steel and comprises internally, bonded thereto, a layer 7 made of a corrosion-resistant material, such as aluminum or stainless steel.

In this manner, the dual need to be able to weld the pipe to the carbon steel structure of the boiler and to protect said pipe against the aggression of the condensation generated in the flue gases is achieved in an optimum manner.

As can be seen from FIG. 1, the layer 7 is present along the entire length of the pipe 6, but it should be clearly noted that such layer might be provided only in the part of the pipe toward the outlet of the flue gases.

An embodiment of the pipe according to the invention is shown in FIG. 3: the carbon steel pipe 8 comprises, bonded thereto, a layer 9 made of corrosion-resistant material and accommodates internally a coaxial sleeve 10, which is closed by at least one plug 10 a, likewise made of corrosion-resistant material.

An interspace 11 for conveying the flue gases in a reduced cross-section is thus provided: the consequent increase in speed effectively helps to increase heat exchange between the flue gases and the water to be heated.

A further increased efficiency of said exchange occurs in the variation of FIG. 4, in which a carbon steel pipe 12 has, bonded thereto, a layer 13 of corrosion-resistant material, and a sleeve 14, closed by a plug 14 a, has ribs 14 b which extend monolithically from it and which, by entering an interspace 15 through which the flue gases flow, make contact with the layer 13, transmitting thereto, and ultimately to the water to be heated, heat by conduction.

An identical situation occurs in the variations of FIGS. 5, 6, 7, and 8, changing only the shape of the cross-section of the ribs: while the ribs of the solution of FIG. 4 are shaped so as to have a cross-section with a rounded cusp, the ribs of the variations of said figures respectively have a rectangular cross-section 16, a triangular cross-section 17 in which the thickness decreases gradually toward the central region 18, and a rectangular cross-section with an end face 19.

The variation of FIG. 9 provides, bonded to a carbon steel pipe 20, a first layer 21 made of corrosion-resistant material, and a second layer 22, also made of corrosion-resistant material, which provides ribs 22 a adapted to make contact, by entering an interspace 23 through which the flue gases flow, with a sleeve 24 closed by a plug 24 a, thus providing a situation which is similar to the one described earlier.

Variations of the cross-sections of the ribs identical to the ones shown in FIGS. 5, 6, 7, 8 are visible in FIGS. 10, 11, 12, 13: therefore, there is no need to deal with these variations.

The variations of FIGS. 14 to 18 replicate the constructive embodiments shown in FIGS. 9 to 13, with the only difference related to the fact that there is just one layer made of corrosion-resistant material bonded to the carbon steel pipe: thus, for example, the variation of FIG. 14 provides, bonded to a carbon steel pipe 25, only a layer 26 made of corrosion-resistant material, which is provided with a ribs 26 a which make contact with a sleeve 27.

FIG. 19 illustrates an embodiment in which a first layer 29, made of corrosion-resistant material, and a second layer 30, also made of corrosion-resistant material, are bonded to a carbon steel pipe 28; ribs 30 a protrude from said second layer and are alternated with ribs 31 a which protrude from a sleeve 31, leaving spaces 32 between said ribs for the flow of the flue gases: ribs 31 a extend until they make contact with the layer 30 in the presence of references 31 b which ensure correct positioning.

A variation of the embodiment of FIG. 19 is shown in FIG. 20: the only difference is the absence of the layer 29 bonded to a carbon steel pipe 33, and therefore only a layer 34 made of corrosion-resistant material and provided with the ribs as described above, is present.

The variation shown in FIG. 21 is now described: it comprises, bonded to a carbon steel pipe 35, a layer 36 made of corrosion-resistant material, which is provided with variously shaped ribs 36 a arranged alternately with respect to variously shaped ribs 37 a which protrude from a sleeve 37 and are adapted to make contact in the presence of references 37 b with the wall of the layer 36.

Another variation is described with reference to FIG. 22, in which the reference numeral 38 designates a carbon steel pipe, which comprises internally two flue gas conveyance modules, designated generally by the reference numerals 39 and 40 respectively, which are delimited by a closed wall made of corrosion-resistant material.

The wall of the module 39 comprises a portion 41, which is bonded to the wall of the pipe 38 substantially along half of the circumferential extension thereof, and a straight portion 42, which extends transversely, and likewise the wall of the module 40 comprises a portion 43 bonded to the wall of the pipe 38 and a straight portion 44; the straight portions 42 and 44 are in mutual contact.

The described configuration allows to obtain the dual result of protecting the wall of the pipe 38 against contact with the flue gases, and this is done by the portions 41 and 43 of the walls of the modules, and of providing an intense transmission of heat from the flue gases to the water contained in the boiler which strikes the outer surface of the pipe 38, determined by the presence of the portions 42 and 44 of said walls which make contact with the flue gases at the region where said flue gases have a particularly high temperature.

FIG. 23 illustrates another variation of the invention, which provides, inside the pipe 38, six flue gas conveyance modules which are substantially shaped like wedges and are designated respectively by the reference numerals 45, 46, 47, 48, 49, 50.

The walls of the module, which are made of corrosion-resistant material, are identical and comprise an arc-like portion, 45 a for the module 45, bonded to the wall of the pipe 38, and two straight portions 45 b, 45 c for said module, which protrude from the ends of said arc-like portion toward the axis of said pipe; the straight portions of the individual modules are in mutual contact.

Of course, this embodiment, too, ensures the functional characteristics stated with reference to the embodiment shown in FIG. 22.

As regards the variation of FIG. 24, it differs from the embodiment of FIG. 23 only in that inside the pipe 38 there are twelve flue gas conveyance modules 51 instead of the six modules provided in the embodiment of FIG. 23.

The variation shown in FIG. 25 provides for the presence, inside the pipe 38, of a continuous layer 52, provided with protrusions such as 53 which protrude toward the axis of the pipe and thus provide, as in the previously described variations, optimum conditions both as regards the protection of the pipe 38 against corrosion and for high efficiency in heat transfer from the flue gases contained in the pipe 38 to the water to be heated.

The described invention is susceptible of numerous other modifications and variations, all of which are within the scope of the appended claims: thus, for example, it is important to stress the fact that the various means for protecting the carbon steel pipe made of corrosion-resistant material may cover different lengths within the described pipes.

The disclosures in Italian Patent Applications No. MN2005A000023 and No. MN2006A000012 from which this application claims priority are incorporated herein by reference. 

1-24. (canceled)
 25. A protected carbon steel pipe for fire tube heat exchange devices, particularly boilers, comprising internally, at least along a portion of the length of the pipe, at least one bonded layer of corrosion-resistant material.
 26. The pipe according to claim 25, further comprising internally a single bonded layer of corrosion-resistant material.
 27. The pipe according to claim 25, further comprising internally a double bonded layer of corrosion-resistant material.
 28. The pipe according to claim 25, further comprising internally a closed coaxial sleeve made of corrosion-resistant material, which is adapted to form an interspace for the flow of the flue gases.
 29. The pipe according to claim 25, further comprising internally a closed coaxial sleeve made of corrosion-resistant material, which is adapted to form an interspace for the flow of the flue gases, the outer surface of the sleeve and the surface of the layer that faces it being both smooth.
 30. The pipe according to claim 25, further comprising internally a closed coaxial sleeve made of corrosion-resistant material, which is adapted to form an interspace for the flow of the flue gases, ribs being provided which protrude monolithically from the sleeve or the surface of the layer that faces the sleeve and are adapted to make contact with the surface of the layer that faces it or with the surface of the sleeve respectively.
 31. The pipe according to claim 30, wherein the ribs have a cross-section shaped like a rounded cusp.
 32. The pipe according to claim 30, wherein the ribs have a rectangular cross-section.
 33. The pipe according to claim 30, wherein the ribs have a triangular cross-section.
 34. The pipe according to claim 30, wherein the ribs have a cross-section which in terms of thickness decreases gradually toward the central region.
 35. The pipe according to claim 30, wherein the ribs have a rectangular cross-section with an end face.
 36. The pipe according to claim 25, comprising internally a closed coaxial sleeve made of corrosion-resistant material, which is adapted to form an interspace for the flow of the flue gases, ribs being provided which protrude alternately from said sleeve and from the surface of the layer that faces it, the ribs that protrude from the sleeve being adapted to make contact in the presence of a reference with said surface.
 37. The pipe according to claim 25, further comprising internally a coaxial sleeve made of corrosion-resistant material, which is provided with variously shaped ribs which are adapted to make contact in the presence of a reference with the surface of the layer that faces the sleeve, said ribs being arranged alternately with respect to variously shaped ribs which protrude from said surface.
 38. The pipe according to claim 36, wherein the at least one layer of corrosion-resistant material and the sleeve cover the entire length of the pipe.
 39. The pipe according to claim 36, wherein the at least one layer of corrosion-resistant material and the sleeve cover partially the inside of the pipe.
 40. The pipe according to claim 36, wherein the at least one layer of corrosion-resistant material and the sleeve cover different lengths inside the pipe.
 41. The pipe according to claim 25, comprising internally, at least in one portion of its length, a bonded layer made of corrosion-resistant material which is provided with protrusions which protrude toward an axis of said pipe.
 42. The pipe according to claim 25, further comprising internally at least two consecutive modules for conveying the flue gases, each module being delimited by a closed wall made of corrosion-resistant material which comprises a portion bonded to the wall of the pipe and at least one portion which protrudes toward an axis of said pipe.
 43. The pipe according to claim 25, further comprising internally two flue gas conveyance modules, each module being delimited by a closed wall made of corrosion-resistant material, which comprises a portion which is bonded to the wall of the pipe substantially along half of a circumferential extension thereof, and a straight portion which protrudes transversely, the straight portions of the wall of the two modules being in mutual contact.
 44. The pipe according to claim 25, further comprising internally a plurality of flue gas conveyance modules, each module being delimited by a closed wall made of corrosion-resistant material which comprises a portion bonded to the wall of the pipe and two straight portions which protrude from the ends of said portion bonded to the wall toward an axis of said pipe, the straight portions of the wall of two consecutive modules being in mutual contact.
 45. The pipe according to claim 25, further comprising internally a continuous bonded layer of corrosion-resistant material, which is provided with straight protrusions which protrude toward an axis of said pipe.
 46. The pipe according to claim 25, wherein the corrosion-resistant material is an aluminum alloy.
 47. The pipe according to claim 25, wherein the corrosion-resistant material is stainless steel. 